The ability to perceive relationships between objects (visuospatial skills) may decline years before a person is diagnosed with Alzheimer's disease, a new study suggests.

It included 444 people who were dementia-free when they were enrolled in the study and underwent tests on a number of cognitive abilities, including visuospatial skills. The assessments were repeated at least once before the end of the study. After an average follow-up of 5.9 years, 134 participants had developed dementia. Of those, 44 underwent brain autopsies that confirmed they had Alzheimer's disease.

The researchers used data from the cognitive assessments to chart declines in various areas before participants were diagnosed with dementia. They found an inflection point (sudden change to a steeper slope of decline) in visuospatial abilities three years before clinical diagnosis of dementia.

Declines in overall cognition occurred the next year, while inflection points for verbal and wroking memory weren't seen until one year before diagnosis.